Arrays and Logic• Let’s generate 6 lotto numbers using a loop and the

random number generator – but we don’t want to duplicate any numbers– how do we know if a number has already been generated? Random generator = new Random( );int[ ] numbers = new int[6];for(int j=0;j<6;j++) { // j keeps track of which number we are going to generate do {

temp = Math.abs(generator.nextInt( ))%48 + 1; // found = false; k = 0; while(!found && k < j) if(numbers[k]==temp) found = true; else k++; } while(found); numbers[j] = temp;}

Multiple Images• Here, we create an array of ImageIcons and

place them all on the screen as thumbnailsImageIcon[] imageIcons = new ImageIcon[12];Image[] images = new Image[12];String filename; // assume all images are in images/pic1.jpg, pic2.jpg etcfor(int i=0;i<12;i++){

filename = "images/pic" + i + ".jpg";imageIcons[i] = new ImageIcon(filename);images[i] = imageIcons[i].getImage();

}int xPosition = 0, yPosition = 0;for(int i=0;i<12;i++){

xPosition = (i%4) * 50;yPosition = (i/4) * 50;g.drawImage(images[i], xPosition, yPosition, 45, 45, Color.black, this);

}

Representing Variable Players• Now lets consider if we want to change our simple game

to allow for between 2 and 5 players– We can’t implement p1, p2, p3, p4, p5 because, while that

seems simple, it would be awkward to determine whose turn it is next in the case of having 3 players, or 2 players, or 5 players

– So instead, we will use an array of players, p[i] storing the location of player i

– We will store the number of players in a variable, n, and use a for loop to control whose turn it is

– So, here we have a revised version of the BoardGame program at http://www.nku.edu/~foxr/Camp08/Programs/BoardGame2.java

Storing Graphics Data in an Array

Random generator = new Random();int i, red, green, blue;int[] x, y, size;Color[] color;x = new int[25];y = new int[25];size = new int[25];color = new Color[25];for(i=0;i<25;i++) {

x[i]=generator.nextInt(480) + 10;y[i]=generator.nextInt(480) + 10;size[i]=generator.nextInt(10) + 3;red=generator.nextInt(256);green=generator.nextInt(256);blue=generator.nextInt(256);color[i]=new Color(red, green, blue);

}g.setColor(Color.black);g.fillRect(0,0,500,500);for(i=0;i<25;i++) {

g.setColor(color[i]);g.fillOval(x[i], y[i], size[i], size[i]);

}

We use 4 arrays•x, y for the <x, y> coordinate•size for the size of the oval•color to store the Color of the oval

Arrays for Random Storage• Another way to use an array is to create an

array with dozens, hundreds or thousands of items and then randomly select from them

• As an example, imagine a hangman game– You want to randomly select a word to use• String[ ] words = {“word1”, “word2”, “word3”, “word4”,

“word5”, “word6”, “word7”, “word8”};

– Now you want to withdraw a word from words– Use a random number generator to get a legal index

from 0 to the length of the array• String word = words[generator.nextInt(words.length)];

– Here, word is one of the 8 words in the array

Millionaire Game• The game of Who Wants to be a Millionaire uses hundreds

of questions from which a few are randomly chosen– String[ ] questions = {“question 1”, “question 2”, …};

• We can randomly generate a question to ask the user, but in the game, the user is also given 4 possible answers

• For our game, we can either use questions whose answers will always be something simple like “yes/no”, “true/false” or 1-word answers, as in– String[ ] questions = {“Who was the first president of the

US?”, “Can ducks fly?”, “In which season does Labor Day fall?”};

• or we can also add our answers to the questions as in• String[ ] questions = {“Which US president served the longest

term, A. Washington, B. Franklin, C. Roosevelt, D. Kennedy?”, “Which of the following birds cannot fly? A. Robin, B. Goose, C. Duck, D. Ostrich”};

Continued• The code might look something like this:– Random g = new Random( );– String[ ] questions = {“question1”, “question2”, …};– char[ ] answers = {‘D’, ‘A’, …};– int j;– char userGuess;– while(!done) {

• j=g.nextInt(questions.length);• System.out.println(“Your next question is:\n” + questions[j]);• userGuess = JOptionPane.showInputDialog(“What is your

answer?”).toUpperCase( ).charAt(0);• if(userGuess==answers[j]) {…// user is right}• else { done=true; … //user is wrong}• }

Continued• What do we do if they are right?

– Increment the level– Add to their winnings– Output that they are right

• What do we do if they are wrong?– Set winnings to 0– Set done to true so that we can exit the while loop– Output that they are wrong

• After the while loop, we need to– Output how much they have won, or if they lost, output some

message to indicate that they lost and have no money• We can also let the user exit the game by “walking away” – for

this, they need to be able to input the walk away choice, for a multiple choice question, ‘E’ for exit, for a String based answer, “exit” or “quit”

• You will implement parts of this as an activity and the remainder as today’s project